Birmingham's 52-mile Northern Beltline will cost $4.7 billion to build according to a new estimate, a big jump from the previous price of $3.4 billion issued in late 2009.

According to Alabama Department of Transportation officials, the new cost estimate was developed in conjunction with the Federal Highway Administration, which is asking states to review major projects to account for price inflation over time and other factors that have caused cost overruns on projects across the country.

The latest estimate puts the total cost of the freeway at an average of about $90 million per mile over the 25-year life of the project.

Opponents say the new price tag should prompt a re-evaluation.

"With all that is going on in Washington and Montgomery about the budget, I am alarmed that the projected cost, which was already so astronomical, has jumped even higher," said Pat Feemster, a member of Save Our Unique River, Communities and Environment, or SOURCE. "It is irresponsible to build a road that is not needed, not justified by traffic needs and will do such damage to the environment."

Proponents were surprised by the cost jump, but said it only points to the need to get the beltline built as quickly as possible.

"While I can't speak to the accuracy of the Federal Highway Administration's new cost estimate for the Northern Beltline, I do know this is a critical infrastructure project for our state, and I will continue to work to fund it expeditiously," said Sen. Richard Shelby, R-Ala. "Escalating costs are just one more reason why we need to get this project under way and completed as quickly as possible."

Rep. Spencer Bachus, R-Vestavia Hills, agreed: "The completion of the Northern Beltline is a high priority for the Birmingham region and retains my total support."

Plans call for the new freeway to branch off Interstate 59 near the Jefferson-St. Clair County border and arc across north Jefferson County, crossing I-65 north of Gardendale, then dropping southwest, crossing Corridor X and eventually connecting to I-20/59 at the western end of I-459.

Proponents say that project is a logical complement to I-459, the southern beltline, and would open large areas of northern and western Jefferson County to suburban, commercial and industrial development.

Opponents say that the proposed path of the road would do little to relieve traffic congestion and is not justified as a transportation project. It would also cross the headwaters of the Cahaba River and Turkey Creek, which environmentalists fear could lead to water pollution problems.

Despite the rising cost estimate, the beltline does have a dedicated source of federal funding.

Sen. Shelby had the beltline designated as part of the Appalachian Development Highway System, tapping a pot of road money separate from the state's general allocation of federal highway dollars.

Currently, the state gets about $117 million a year from the ADHS. That money is being used to connect Corridor X to I-65 and U.S. 31, and finish two smaller projects in North Alabama. When those projects are complete, the full allocation, plus the 20 percent state match, could be available for the beltline.

However, it is unclear how much the state will receive from ADHS going forward. Congress is currently drawing up new budgets and a new transportation bill. Funding levels set there will in turn determine the amount available for the beltline.

Vaughn was involved in planning Corridor X, the soon-to-be-completed link between Birmingham and Memphis that will become I-22. In 1977, the estimate for that 100-mile interstate link in Alabama was $100 million, which at the time was a shocking number. Thirty-four years later, the actual cost of Corridor X looks to be around $1 billion.

ALDOT has a plan to build the beltline over 25 years, Vaughn said. However, the pace of construction will be dependent on the flow of federal dollars.

If the new cost estimate is accurate over the life of the project and money from the AHDS doesn't increase, it would take more than 32 years' worth of appropriations to complete the road.

Darrell Howard, deputy director of transportation planning at the Birmingham Regional Planning Commission, said that transportation planners have been aware for some time now of a troubling trend in highway financing.

As the fuel economy of cars and trucks has increased, the amount generated by fuel taxes have remained relatively flat, especially compared to increasing costs for construction, land and highway maintenance.

"If we assume federal money stays the same, there won't be enough money," Howard said. "We are running out money .¤.¤. It is something we have known was coming for a long time."

But Barry Copeland, the interim president of the Birmingham Business Alliance, said he is confident the state's congressional delegation will keep the project moving. Copeland said the increased cost estimate is not a reason to rethink the project.

"It is impossible to predict how much funding will be available, but I think the project is feasible to do and it is extremely necessary," he said. "It's absolutely important to the economic development to the northern half of Jefferson County. Wherever you put that route, economic development will follow. And the time to start it is now."

Eva Dillard, staff attorney for Black Warrior Riverkeeper, disagrees.

"With the national debt now over $14 trillion, we are at a loss to understand how beltline boosters can reconcile their support for this one project with their pledges to cut federal spending in Washington," Dillard said. "We want to see sensible, sustainable economic development initiatives for our region, not harmful projects like the beltline, which fragment communities and destroy natural resources."